Lightning surges, switching surges and electromagnetic pulses (EMP) are usually the source triggering abnormal interference or power failure in electrical equipment. The three types of interference sources usually intrude upon electrical equipment via a power supply circuit, a signal circuit (control circuit) or the ground of a circuit. If lacking a sufficient ability or appropriate means to process surge energy or discharge current, equipment is prone to fault or interference. To this end, many electronic devices, communication devices, control devices and power supply devices are equipped with surge suppression devices as a countermeasure. Among them serial surge suppression and overload protection optimization devices are characterized by absorbing transient overvoltages, overcurrents and high surge energies in practical applications and achieving the objective of effectively preventing equipment disruptions and failures.
New generations of serial surge suppression optimization devices further have a counter capable of detecting the number of surge or EMP attacks upon a device. Besides an internal load-sharing design incorporating multiple serial surge suppression optimization devices that are parallelly connected for the load-sharing purpose so as to increase load currents, the new generations of serial surge suppression devices further have many practical functions and designs, such as automatic overload protection, display, detection and recovery of automatic bypass detection and the like.
However, the detailed design of the foregoing conventional serial surge suppression and overload protection optimization devices needs to be further improved. The most critical disadvantages are as follows.
1. The foregoing serial surge suppression and overload protection optimization devices mainly employ metal oxide varistor (MOV) therein as a surge protection element to process surge energy. When attacked by a surge, the conventional MOV may be shorted by way of two terminals thereof melting together after absorbing the surge energy. The consequence is that a short circuit occurs between the line wire (L) and the neutral wire (N), the line wire (L) and the ground (G) or the neutral line (N) and the ground (G). As a result, the serial surge suppression and overload protection optimization devices break down and fail to normally supply power after a surge attack.
2. After the MOV melts and is shorted, the foregoing serial surge suppression and overload protection optimization devices totally loses the surge suppression capabilities and fails to further provide any secondary surge protection capabilities after a surge attack.
3. The internal design of the foregoing serial surge suppression and overload protection optimization devices fails to accurately detect, adjust and control the magnitude of the overload current.